The Automatic Identification System (AIS) is a modern navigation tool used on ocean-going vessels. AIS allows for the exchange of data regarding the position and movement of vessels, enhancing safety at sea and improving maneuverability and visibility under various conditions. As part of the Global Maritime Distress and Safety System (GMDSS), AIS data is automatically recorded by the Voyage Data Recorder (VDR), enabling analysis during emergencies. This article presents the functions of AIS, differences between classes, its advantages and disadvantages, and specialized rescue devices such as AIS SART and AIS EPIRB.

How the AIS System Works

AIS operates by automatically transmitting data on dedicated frequencies (161.975 MHz and 162.025 MHz) via a VHF antenna, allowing for easy tracking of vessels within range. AIS is equipped with an internal GPS receiver with its own antenna to determine the vessel’s position in case of a failure of the primary GPS system. The AIS system also receives data from other navigational sources, such as:

  • External GPS System: AIS primarily receives data from an external GPS system to accurately determine its position.
  • Gyrocompass: AIS receives directional data, allowing for more precise course determination.
  • Echo Sounder: The echo sounder provides information on the water depth beneath the vessel, which is crucial for safe navigation.
  • Speed Log: AIS utilizes speed data relative to the water, which is important during maneuvers and monitoring the vessel’s course.

AIS regularly transmits the received data to various onboard devices, such as the VDR, radar, and Electronic Chart Display and Information System (ECDIS). Transmitting AIS data to radars and ECDIS allows the crew to track vessels on screen, facilitating collision avoidance and navigation in tight waters or areas with heavy traffic.

Main Functions of the Automatic Identification System (AIS)

AIS performs several critical functions that support safe navigation:

  • Vessel Identification: AIS transmits information such as the vessel’s name, MMSI number, GPS position, course, and speed, enabling quick recognition of nearby vessels.
  • Movement Tracking: AIS provides real-time monitoring of vessel movement and trajectory prediction, which is crucial for collision avoidance.
  • Vessel Status: The system transmits operational status information, such as whether the vessel is anchored or underway.
  • Communication Between Vessels: AIS also features a short message exchange function, allowing direct and rapid communication between ships without using public VHF radio channels.
  • Recording in VDR: All AIS data is automatically recorded by the VDR, providing the opportunity for analysis if event reconstruction is necessary.

With integration from the gyrocompass, echo sounder, GPS system, and speed log, AIS provides more accurate navigational data. This information can be passed to other navigational systems on board, such as radar and ECDIS, ensuring better traffic management and enhancing navigational safety.

AIS Class A vs. AIS Class B

AIS is available in two classes – A and B – each having different technical specifications and applications for various types of vessels.

  • AIS Class A: Used on larger commercial and passenger vessels. It has a higher transmission priority, greater power output, and provides more precise position updates every 2 to 10 seconds (depending on the vessel’s speed). Class A AIS allows for accurate real-time monitoring of vessel movements.
  • AIS Class B: Primarily used on smaller vessels, such as yachts and recreational boats. It features a lower transmission priority and reduced power output, limiting its effectiveness in crowded areas. Position updates are transmitted every 30 seconds, which is sufficient for vessels operating in calm coastal waters.

Class A AIS is more advanced and suitable for larger vessels, while Class B AIS is effective for smaller vessels that do not need to monitor their position as frequently and operate in less congested areas.

Advantages and Disadvantages of the AIS System

Advantages of AIS:

  • Increased Safety at Sea: AIS reduces the risk of collisions, especially in high-traffic areas like ports.
  • Easy Vessel Identification: The AIS system allows for quick identification of nearby vessels, benefiting both the crew and traffic management services.
  • Inter-Vessel Communication: The ability to send short text messages enables vessels to quickly warn each other of course changes or maneuvers.
  • Historical Data: AIS records data, which is useful for investigations following accidents or collisions.

Disadvantages of AIS:

  • Visibility for All Users: AIS is an open system, meaning any vessel with a receiver can track the position of others, which can pose privacy and security concerns.
  • Range Limitations: AIS operates effectively only where shore-based or satellite receivers are available.
  • Lack of Obstacle Detection: AIS provides information about other vessels but does not detect physical obstacles, such as rocks or drifting objects, limiting its functionality.

Differences Between AIS Targets and Radar Targets

AIS and radar are two different yet complementary navigation systems. AIS provides detailed information about vessels equipped with AIS, while radar detects all objects within range, regardless of whether they have an AIS transponder.

  • AIS Targets: Provide detailed data about vessels equipped with AIS, such as identification, course, and speed.
  • Radar Targets: Radar detects all objects in its range, including vessels with AIS and those without a transponder (e.g., buoys, shorelines, drifting objects). Radar is reliable in detecting physical obstacles but does not provide detailed data about vessels.

Combining AIS and Radar gives the most comprehensive view of the navigational situation, allowing for better traffic management and minimizing collision risks.

AIS SART and AIS EPIRB

AIS also includes specialized emergency devices, such as AIS SART and AIS EPIRB, which enhance safety in emergencies.

  • AIS SART (Search and Rescue Transponder): This device is used in emergency situations and emits a signal received by nearby vessels, facilitating the location of survivors or distressed units.
  • AIS EPIRB (Emergency Position Indicating Radio Beacon): Similar to standard EPIRBs but using the AIS signal, allowing for immediate alerts to nearby vessels. AIS EPIRB is particularly useful in crowded maritime areas, enabling rapid and precise location of endangered vessels.

Tracking Vessels Online

Real-time positions of vessels can be tracked using MarineTraffic.com. Sharp Horizon is part of the MarineTraffic community, supporting maritime traffic monitoring in the Baltic Sea. Our AIS station located in Szczecin is available at here, allowing for ongoing monitoring of vessel traffic and position analysis.

Summary

The Automatic Identification System (AIS) is a vital tool in modern maritime navigation. It enhances safety, ensures efficient communication between vessels, and improves maritime traffic management. Classes A and B AIS offer various functions tailored to the needs of different-sized vessels, while the combination of AIS with radar provides a complete picture of the navigational situation. With its messaging capabilities, integration with onboard devices like GPS, gyrocompass, and echo sounder, AIS offers better control over vessels and enables immediate response in emergency situations.

For more information about AIS technology and other navigational systems, visit our BLOG.